Unless you can pass for a young teenage male and are willing
to don a hat and a posh accent, it's unlike you're going to
get into the Harrow school swimming pool. Mere citizens must
pay to swim and you can do so in Wealdstone at the Harrow leisure
centre or at the Hatch end swimming pool.
Harrow leisure centre, Christchurch avenue,
Wealdstone
A map is available here
Hatch end swimming
pool, Uxbridge road, Hatch end